The invention relates to circuit arrangements in coin acceptors.
Circuit arrangements in coin acceptor units, are know in the prior art, for accepting a coin whenever it causes the oscillation waves to stop, as well as circuit designs in which an inserted coin is accepted whenever it causes the oscillation to start. The circuit arrangement according to the principles of the present invention operates with the identical method as the first mentioned systems, in which the effect of the influence on the magnetic (or electric) field causing a reduction of the oscillation amplitude serves as the test criterion. However, in this invention, the coin is placed, instead of into the field of the self-induction coil of the oscillator, into the r.c. coupling field between a primary and a secondary r.c. coupling, causing an acceptance signal for the coin dependent on the reduction of the degree of the r.c. coupling caused by the coin, i.e. dependent on the reduction of the amplitude of the signal received.
It is the aim of any coin-testing apparatus to distinguish acceptable from non-acceptable coins as precisely as possible. In order to achieve this goal, it would be necessary, for instance, with the first mentioned circuit arrangement, to determine the attenuation limit of the oscillator which would be decisive for the test, and in which the oscillations would cease, exactly corresponding to the lower limit value of the range of conductivity of acceptable coins. Thus far, this has not been done, but a relatively large area of tolerance has been provided. This was necessary, because the limit conditions in which the oscillations start or cease, respectively, depend on the temperature and other influences. The resistance of the coil of the oscillator, for instance, and the transistor amplification depend on temperature conditions; in addition, metal residue inside of a dirty coin slot have an influence on the coil field and thereby on the attenuation.
The invention is based on the task of more exactly limiting the test tolerance range to the permissible range of tolerance for acceptable coins and on avoiding additional tolerances for changes in temperature and other influences.
It is the object of the present invention to provide a circuit in which the values determining the amplification are stored as amplification values, thus, for instance, the value of a control voltage regulating the amplification, or the reverse feedback--or feedback ratio or, respectively, the values of the resistances which influence the control voltage, the reverse feedback--or the feedback ratio.
In the circuit arrangement according to the invention, the standard value of the amplification indicates the very amplification with which, given normal conditions, the oscillations will cease or commence, respectively, whenever there is no coin in the area of the coil field. The oscillating circuit in this case may be attenuated either alone by its characteristic attenuation or by the additional hook-up of a resistor, which is not hooked up during the coin testing process. The resistor, in this instance, is so designed that it causes at least approximately the identical attenuation as an acceptable coin. If several types of coins must be tested, it is practical to design the resistor so that the attenuation it effects is approximately in the middle of the range of the attenuations caused by the various types of coins. In the preferred embodiment, therefore, the standard value of the amplification and the value of the amplification for an attenuation of the oscillating circuit existing prior to each coin testing procedure are determined, the attenuation approximating that caused by acceptable coins. With the preferred embodiment of the invention, therefore, it is possible to obtain nominal limit values of amplification, corresponding exactly to the prevailing conditions, if the relative change of the attenuation caused by operational conditions which deviate from normal conditions is not dependent on the total attenuation.
The same applies to the modified circuit arrangement of the invention.
Using the accompanying drawing, preferred embodiments of the invention are described in detail, in the specification hereinafter following.